Liquid crystal/polymer composites, such as those used to form polymer dispersed liquid crystals (PDLCs) and polymer stabilized cholesteric texture (PSCT) light shutters, have been used to make flexible displays, transparent displays and switchable windows. In a PDLC, the concentrations of the polymer and the nematic liquid crystal material in the composite are comparable; however, the nematic liquid crystal exists in isolated droplets that are dispersed in the polymer, such that the droplet size is comparable to the wavelength of visible light. During operation in the voltage-off state, the liquid crystal inside the droplets orients randomly throughout the PDLC material. Thus, when light propagates through the PDLC material, the encountered effective refractive index in the liquid crystal droplet is different from the encountered refractive index np in the polymer, causing the light to scatter through the material, and as a result, the PDLC material appears opaque. When a sufficiently high electric field is applied across the PDLC material, the liquid crystal inside the droplets is aligned uniformly along the applied field (film normal direction). Thus, in the case of normal incident light, when it propagates through the liquid crystal droplet, the effective refractive index encountered by the light propagating through the PDLC material is the ordinary refractive index n0 of the liquid crystal, which is matched to the refractive index np of the polymer. As a result, the light is permitted to be transmitted through the PDLC material causing it to become transparent.
In a polymer stabilized cholesteric texture (PSCT) light shutter, the polymer concentration of the composite material is usually less than 5%, and it exists in the form of anisotropic networks, which are dispersed in a cholesteric liquid crystal. The liquid crystal exists in domains with a size comparable to the wavelength of visible light. In one voltage state, the orientation of the liquid crystals in the domains is random in the PSCT material, such that the refractive index changes from domain to domain resulting in a material that is light scattering. In another voltage state, the liquid crystals in domains are uniformly aligned in one direction, and as a result, the refractive index of the PSCT material does not vary, allowing the material to become transparent. Thus, the PSCT material can be switched between a light scattering state and a transparent state by applying the appropriate voltage or lack of voltage to the PSCT material.
Furthermore, polymer dispersed liquid crystals (PDLCs) are self-adhesive, can be easily manufactured by a roll-to-roll process, and may be formed to take up a large area. Unfortunately, PDLCs have a limited viewing angle because the refractive indices of the polymer and the liquid crystal are only matched for light incident on the cell (substrate) in a normal direction. In contrast, polymer stabilized cholesteric texture (PSCTs) liquid crystals have a large viewing angle, because the liquid crystal and the dispersed polymer network are aligned in the same direction in the transparent state, and because their refractive indices are matched for light incident in any direction. However, it is difficult to manufacture PSCTs using a roll-to-roll manufacturing process because of the low viscosity of the liquid crystal/monomer composite mixture.
Therefore, there is a need for an encapsulated polymer stabilized cholesteric texture (EPSCT) light shutter that is self-adhesive. In addition, there is a need for an encapsulated polymer stabilized cholesteric texture light shutter that has a large viewing angle. Furthermore, there is a need for an encapsulated polymer stabilized cholesteric texture light shutter that can be manufactured using a roll-to-roll process. Moreover, there is a need for an encapsulated polymer stabilized cholesteric texture light shutter that combines the benefits of a polymer dispersed liquid crystal (PDLC) and a polymer stabilized cholesteric texture (PSCT) device.